The present invention relates to a data display control system in a raster-scan-type display device having a frame memory, and more particularly to a data display control system wherein a plurality of data are displayed simultaneously on a display surface of one display device so as to constitute a multiplex display surface.
In recent years, interactive operation using a display device has become a significant part of personal computer processing as well as various other instruments designed for processing data. In such situations, the simultaneous display of a plurality of data onto one display device becomes an important problem to solve in order to make the operation of such instruments by a user easy and efficient. Various companies of Japan and foreign countries have offered solutions to this problem. A specific example of a multi-window display control system is described in detail in Gregg Williams, "The Lisa Computer System", BYTE, Feb. 1983, p. 33-50.
In systems similar to the Lisa computers, multi-window display control systems, a major disadvantage is how efficiently the overlapped state of the display areas during the output of display data is controlled, and how rapidly the overlapped state is processed during operation of the display areas and the display data. For example, a common method is that overlapped parts between a new display surface (window) and a plurality of existing display surfaces (windows) are saved per each window. In this method, comparison calculation of coordinate positions of each window frequently occurs, and the number of data transfers for save or recovery increases thereby control of the save state is difficult.